Horizontal gene transfer

horizontal gene transfer is

the movement of genetic elements between cells that are not direct progeny

unlike vertical gene transfer, HGT allows

gene transfer between different bacteria species

horizontal gene transfer may happen in the following ways

conjugation

transformation

transduction

which of the three mechanisms of horizontal gene transfer is considered to have the most significant influence on the spread of antibiotic resistant genes

conjugation

not all horizontal gene transfer produce a cell with

a new combination of genes

the DNA transferred to a new cell can face the following outcomes

• the DNA may be destroyed by DNA restriction enzyme

• the DNA may replicate by itself, independent of the chromosome (ex plasmid)

• the DNA may be incorporated into the chromosome, creating a recombinant

Conjugation is

a DNA transfer between cells through physical contact via pili or adhesion

Conjugation involves

a donor (F+) and a recipient (F-)

a donor

has to carry genes that encode the machinery (sex pili) required to perform the cell-to-cell contact

in most cases, these genes are encoded in conjugative or fertility plasmic

conjugation using sex pili is mainly performed by

gram-negative bacteria

generation of sticky molecules on its surface that brings two cells together is generally done by

gram positive bacteria

step one of conjugation

donor cell (which contains conjugative plasmid) comes in contact with recipient cell (which does not contain conjugative plasmid)

step two of conjugation

the plasmid is replicated during the transfer of a single-stranded copy of the plasmid DNA to the recipient

step three of conjugation

the recipient’s enzymes will synthesize a complementary strand for the transferred plasmid DNA

transformation is

the uptake and integration of extracellular DNA into the cells

cell to cell contact is not required in transformation

in order for transformation to be successful

• the cell should be competent

• the DNA should exist outside of the cell. the DNA can be circular (plasmid) or linear

• after intake, the foreign DNA should be incorporated into the chromosome or stabilized in the form of a plasmid

only a handful of bacterial species are able to perform transformation under

normal bacteria growth condition

bacteria’s competence can be induced by the presence of

peptides, nutritional status, or other stressful conditions such as the presence of antibiotics

transformation is also an important

biotechnology technique

it has been used to insert a gene of interest into a bacterial cell, thus creating a recombinant cell

transduction is

a DNA transfer mediated by bacteriophage

the DNA transfer occurs after the bacteriophage

infects a donor bacteria and carries parts of that bacterias DNA into a new recipient bacteria cell

not all viruses can perform transduction and

not all bacteria are transducible

bacteriophage transfers the DNA either in

generalized or specialized ways

in generalized transfers

any portion of the donor’s genome is carried by the virus

in specialized transfer

DNA from a specific region of the host chromosome is integrated directly into the virus genome